Multi-faceted mems mirror device useful for vehicle lidar

ABSTRACT

An illustrative example MEMS device includes a base and a plurality of mirror surfaces supported on the base. The plurality of mirror surfaces are respectively in a fixed position relative to the base. The plurality of mirror surfaces are at respective angles relative to a reference surface. The respective angles of at least some of the mirror surfaces are different from the respective angles of at least some others of the mirror surfaces.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application and claims the benefit under 35U.S.C. § 120 of U.S. patent application Ser. No. 15/823,726, filed Nov.28, 2017, the entire disclosure of which is hereby incorporated hereinby reference.

BACKGROUND

Advances in electronics and technology have made it possible toincorporate a variety of advanced features on automotive vehicles.Various sensing technologies have been developed for detecting objectsin a vicinity or pathway of a vehicle. Such systems are useful forparking assist and cruise control adjustment features, for example.

More recently, automated vehicle features have become possible to allowfor autonomous or semi-autonomous vehicle control. For example, cruisecontrol systems may incorporate LIDAR (light detection and ranging) fordetecting an object or another vehicle in the pathway of the vehicle.Depending on the approach speed, the cruise control setting may beautomatically adjusted to reduce the speed of the vehicle based ondetecting another vehicle in the pathway of the vehicle.

There are different types of LIDAR systems. Flash LIDAR relies upon asingle laser source to illuminate an area of interest. Reflected lightfrom an object is detected by an avalanche photodiode array. While suchsystems provide useful information, the avalanche photodiode arrayintroduces additional cost because it is a relatively expensivecomponent. Additionally, the laser source for such systems has to berelatively high power to achieve sufficiently uniform illumination ofthe area of interest.

Scanning LIDAR systems utilize different components compared to flashLIDAR. One challenge associated with previously proposed scanning LIDARsystems is that additional space is required for the scanning componentsand there is limited packaging space available on vehicles. Opticalphase array LIDAR systems utilize beam multiplexing that tends tointroduce relatively significant power loss. Liquid crystal waveguideshave even lower efficiency. In either case additional optical componentsare required for alignment and highly precise alignment accuracy isnecessary.

Other aspects of previously proposed LIDAR systems include drawbacks.For example, two-dimensional scanning MEMS (micro-electro-mechanicalsystem) mirrors are not suitable for use in environments subject tovibrations, such as automotive applications. Although one-dimensionalMEMS mirrors are robust against vibrations they require multiple lasersources and respective mirrors to achieve an adequate field of view. Theduplication of components in such systems increases cost and sizerequirements, both of which are considered undesirable.

There is a need for improvements in components for systems, such asLIDAR systems, that are lower-cost, easier to fit within small packagingconstraints, and utilize power efficiently.

SUMMARY

An illustrative example MEMS device includes a base and a plurality ofmirror surfaces supported on the base. The plurality of mirror surfacesare respectively in a fixed position relative to the base. The pluralityof mirror surfaces are at respective angles relative to a reference. Therespective angles of at least some of the mirror surfaces are differentfrom the respective angles of at least some others of the mirrorsurfaces.

Various features and advantages of at least one disclosed exampleembodiment will become apparent to those skilled in the art from thefollowing detailed description. The drawings that accompany the detaileddescription can be briefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a vehicle including a detection devicedesigned according to an embodiment of this invention.

FIG. 2 schematically illustrates selected portions of an example devicedesigned according to an embodiment of this invention.

FIG. 3 schematically illustrates an example embodiment of a MEMS mirrorcomponent.

FIG. 4 schematically illustrates selected features of the embodiment ofFIG. 3.

FIG. 5 schematically illustrates selected features of the embodiment ofFIG. 3 considered along the section lines 5-5 in FIG. 3.

FIG. 6 schematically illustrates selected features of the embodiment ofFIG. 3 considered along the section line 6-6 in FIG. 3.

FIG. 7 schematically shows a performance feature of the illustratedexample embodiment.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a vehicle 20 including a detectiondevice 22. One example use for the detection device 22 is to providesensing or guidance information for a vehicle, engine or brakecontroller, such as an automated vehicle controller. For discussionpurposes, the detection device 22 is a LIDAR device that emits at leastone beam of radiation that is useful for detecting objects in a vicinityor pathway of the vehicle 20. In this example, the beam of radiationcomprises light directed at a selected angle relative to the vehicle 20.

FIG. 2 schematically illustrates selected portions of the detectiondevice 22 including a multifaceted reflector 24. The reflector 24 hasseveral features that are useful, alone or together, for achieving adesired radiation or light pattern, such as a LIDAR beam. The reflector24 provides the stability of a one-dimensional MEMS mirror device yet isable to provide a two-dimensional scanning area while reducing thenumber of components needed for LIDAR applications, reducing oreliminating a need for high precision assemblies, and reducing powerloss. With the reflector 24, the detection device 22 is more efficientfrom a performance and a cost perspective.

The reflector 24 is supported by a support 26 in a manner that allows anactuator or moving mechanism 28 to cause pivotal or rotary movement ofthe reflector 24 about an axis 30 as schematically represented by thearrows 32. Rotary or pivotal movement in this example includesrelatively minor angular changes in the position of the reflector 24,such as 20°, and does not require full rotation about the axis 30. Insome embodiments, the reflector 24 is moveable relative to the support26 while in other embodiments, the moving mechanism 28 causes movementof the support 26 with the reflector 24. The moving mechanism 28 in someexample embodiments includes a known MEMS actuator configuration that iscapable of causing the desired pivotal or rotary motion.

As can be appreciated from FIGS. 2 and 3, the multifaceted reflector 24includes a base 40 and a plurality of mirror surfaces 42 that are fixedrelative to the base 40 and oriented at respective angles relative to areference defined by the base 40. In some examples, a flat, bottomsurface 44 of the base 40 serves as a reference surface for measuring ordefining the respective angles of the mirror surfaces 42. In thisexample, at least some of the mirror surfaces 42 are oriented orsituated at respective angles that are different than the angles of atleast some others of the mirror surfaces 42.

FIG. 4 illustrates one aspect of the arrangement of the mirror surfaces42. The illustrated example embodiment includes the mirror surfaces 42arranged in a chevron pattern including a plurality of chevrons. Thebroken lines in FIG. 4 provide a visual indication of which of themirror surfaces 42 are considered in a particular chevron and are notintended to indicate any physical marking on the reflector 24. Thisexample includes chevrons 50, 52, 54, 56, 58, 60 and 62. In thisexample, the peak of each chevron is centered on the reflector 24 andthe chevrons are symmetric about the longitudinal center of thereflector 24, which coincides with the axis 30 of FIG. 2.

FIG. 5 illustrates one feature of the mirror surfaces 42 in each chevronof this embodiment. The thickness of the reflector 24 varies along therespective chevrons with a greatest thickness near a center or peak ofthe chevron and a smallest thickness near the lateral edges 70, 72 ofthe reflector 24. In FIG. 5, the thickness of the reflector from thebottom surface 44 to the mirror surface 42A is a first thickness t1. Themirror surfaces 42B on either side of the mirror surface 42A are at asecond height established by a second thickness t2 of the reflector 24.The second thickness t2 is smaller than the first thickness t1. Themirror surfaces 42C that are adjacent and lateral to the mirror surfaces42B are closer to the surface 44 and the reflector has a third thicknesst3 at the locations of the mirror surfaces 42C. The third thickness t3is greater than a fourth thickness t4 at the location of the outermostmirror surfaces 42D adjacent to the lateral edges 70, 72 of thereflector 24.

FIG. 6 schematically illustrates another feature of the exampleembodiment considered along the section line 6-6 in FIG. 3. FIG. 6 showsone way in which the respective angles of the mirror surfaces 42 varyalong the reflector 24. A first mirror surface 42E is situated at afirst angle at 80 relative to the reference, which is the bottom surface44 in this example. The broken lines in FIG. 6 are intended to highlightthe respective angles of the mirror surfaces and not to show anymarkings or surface lines on the reflector 24. A second mirror surface42F is situated at a second angle at 82 that is smaller or less steepthan the angle of the first mirror surface 42E. The mirror surfaces42G-42I are respectively at a smaller or less steep angle at 84, 86, 88than the adjacent mirror surface. In one embodiment the angles at 80-86are 63.5°, 61.5°, 58.5°, 57.5°, and 54°, respectively, as measuredrelative to the reference surface 44.

The angles 80-86 increase or become steeper along the reflector in adirection from one end 90 to an opposite end 92 for the mirror surfacesthat are aligned with each other in rows parallel to the lateral edges70 and 72.

The respective angles of the mirror surfaces also increase along eachchevron in a direction from either lateral edge 70, 72 toward the centerof the reflector or the peak of the chevron. Each of the mirror surfaces42 at the center or peak of the corresponding chevron in the center rowof the illustrated example is at a steeper angle compared to any othermirror surfaces in the same chevron. Taking the mirror surfaces 42A-42Din FIG. 3 as examples, the mirror surface 42A is situated at an angle of53°, the mirror surfaces 42B are each situated at an angle of 52°, themirror surfaces 42C are oriented at an angle of 51° and the mirrorsurfaces 42D are at an angle of 50°.

The inter-element angular interval, which is the difference between theangles of adjacent mirror surfaces 42 in the chevrons, varies dependingon how close the corresponding chevron is to the end 90 or 92. Thechevrons 50 and 52, for example, are closer to the end 90 and have agreater inter-element angular interval compared to the other chevrons.The chevron 62, which is closest to the end 92, has the smallestinter-element angular interval. As mentioned above, the mirror surface42 in the center or peak of the corresponding chevron is at a steeperangle compared to those closer to the lateral edges 70, 72 of thereflector 24. The inter-element angular interval in the chevrons 50 and52 includes a full degree difference between each adjacent two mirrorsurfaces in the corresponding chevron and a total angular difference ofthree degrees between the steepest and shallowest angles of thecorresponding chevron. The angle of the mirror surface 42A is threedegrees greater than that of the mirror surfaces 42D in this example.

In the chevron 62, for example, the inter-element angular interval isone-half of one degree among adjacent mirror surfaces in that chevron.The mirror surface angle at the center of the reflector and the peak ofthe chevron 62 is 65° and the mirror surface angle of the mirrorsurfaces at the edges 70 and 72 is 63.5° for a total angular differenceof 1.5° along the chevron 62.

The inter-element angular interval also varies among the mirror surfacesin corresponding rows aligned with the lateral edges 70, 72. The angulardifference between adjacent mirror surfaces 42 in the same row andcloser to the end 90 is as much as 4° in the illustrated exampleembodiment while the inter-element angular interval is 2° betweenadjacent mirror surfaces 42 closer to the end 92.

In the illustrated example, the angles of the mirror surfaces 42 rangefrom 45° to 65° relative to the surface 44 as a reference. Those skilledin the art who have the benefit of this description will realize whatspecific angles will meet their particular needs. Having multiple anglesprovides coverage over a selected beam width or angle in at least onedirection. A beam for vehicle LIDAR is usually considered to have avertical and a horizontal angular coverage or spread. For example, theangles of the mirror surfaces 42 provide the vertical angular coveragewhile the moving mechanism 28 causes movement of the reflector 24 toprovide the horizontal angular spread.

FIG. 7 schematically shows a source 94 that emits radiation such aslight schematically shown at 96. The mirror surfaces 42 of the reflector24 reflect the light 96 as schematically shown at 98 and spread thatlight across an angular coverage that results from the different anglesat which the mirror surfaces 42 are situated on the reflector 24. Theway in which the mirror surfaces 42 reflect the light as schematicallyshown at 98 provides coverage in one dimension (e.g., vertical) andmovement of the reflector 24 as caused by the moving mechanism 28provides coverage in a second dimension (e.g., horizontal). The movingmechanism 28 moves the reflector 24 about the axis 30 in a manner thateffectively moves or spreads the beam 98 into and out of the page of thedrawing. The moving mechanism 28 moves the reflector at a high frequencyscanning rate in the example embodiment.

The end 90 of the reflector 24 is closer to the source 94 than the end92 in the arrangement shown in FIG. 7. The angles of the mirror surfaces42 closer to the edge 90 are more acute or shallower relative to thereference (i.e., the surface 44) and are, therefore, more shallowrelative to the source 94. The mirror surfaces 42 that are further fromthe source 94 and closer to the end 92 of the reflector 24 are atsteeper angles relative to the source 96. For example, the mirrorsurfaces 42 closest to the source may be at 45° relative to thereference. The mirror surfaces furthest from the source 94 may be at 65°relative to the reference. The base 40 of the reflector may be at anangle of 45° relative to the direction of light emission from the source94.

As described above, the chevrons 50-54 for example have a largerinter-element angular interval, which provides a larger total angularcoverage compared to the chevrons 58-62 for example, which are furtherfrom the source 94. The shallower angled mirror surfaces 42 nearer tosource 94 project a larger spot compared to the deeper angled mirrorsurfaces 42 further from the source. The example mirror surface anglepattern creates a reflection pattern that covers as much as possible ofthe region within the detector device field of view in one direction(e.g., vertically) without leaving any space uncovered by the reflectedradiation beams in that direction (e.g., the vertical scale).

Compared to a two-dimensional scanning MEMS mirror the reflector 24spreads the beam 98 to cover the required vertical field, for example,so that only one direction of scanning (e.g., horizontal) is required toachieve scanning to cover a two-dimensional field of view or beam range.Known two-dimensional scanning MEMS devices typically require scanningin two directions that limits the frequency of the scanning at a verylow frequency along either of the axes. Control is definitely morecomplex and unstable for such two-dimensional scanning MEMS mirrorscompared to the detector device 22. The illustrated example embodimentof the reflector 24 provides the stability and advantages of aone-dimensional MEMS mirror while also achieving the type of coveragethat is possible with two-dimensional devices as the moving mechanism 28moves the reflector 24 about the axis 30 at a high frequency.

The reflector 24 also has a plurality of peaks 100. The mirror surfaces42 are on one side of each peak 100 and second surfaces 102 are on anopposite side of each peak. In this example the second surfaces 102 aremirrored but in some examples the second surfaces 102 are notreflective. Each mirror surface 42 has two edges 104, 106 extending fromthe corresponding peak 100 toward the base 40. The edges 104 and 106 aresituated at the angle of the corresponding mirror surface 42. The edges104 and 106 of the mirror surfaces 42 are all parallel to each other inthis example and all of the peaks 100 are parallel to each other. Mostof the mirror surfaces 42 are rectangular although at least thoseclosest to the ends 90 and 92 have a more complex geometry.

Embodiments of this invention provide LIDAR scanning capability usefulfor automated vehicles while requiring lower power and occupying lessspace compared to other proposed arrangements. The fixed position of themirror surfaces 42 and the respective angles of them allows forachieving coverage in one field direction and the stability needed toscan at a high frequency in a second field direction.

While the illustrated example embodiment includes various features suchas different ways that the angles of the mirror elements vary along thereflector, not all of those features are necessary to realize thebenefits of embodiments of this invention for all applications. It maybe possible to use some of the inter-element angular intervalconfigurations of the example reflector without using all of them or tovary the pattern of the mirror surfaces from the illustrated example.Those skilled in the art who have the benefit of this description willrealize what other embodiments of this invention will suit theirparticular needs.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed example embodiment andfeatures may become apparent to those skilled in the art that do notnecessarily depart from the essence of this invention. The scope oflegal protection given to this invention can only be determined bystudying the following claims.

I claim:
 1. A MEMS device, comprising: a plurality of mirrors attachedto a same base; the plurality of mirrors forming an arrangement having aV-shape with an apex of the arrangement aligned with an axis of rotationof the base; wherein the plurality of mirrors have progressive angles ofinclination relative to a plane parallel to the axis of rotation.
 2. TheMEMS device of claim 1, wherein the angles of inclination increase fromsides of the base to the apex of the arrangement.
 3. The MEMS device ofclaim 1, wherein a plurality of nested arrangements extend from a firstend of the base to a second end of the base opposite the first end; theapex of each nested arrangement aligned along the axis of rotation ofthe base.
 4. The MEMS device of claim 3, wherein a surface at the firstend of the base has an angle of inclination of zero degrees.
 5. The MEMSdevice of claim 3, wherein the plurality of nested arrangements haveprogressive angles of inclination relative to one another.
 6. The MEMSdevice of claim 5, wherein the progressive angles of inclination of eachof the plurality of nested arrangements increase from the first end ofthe base to the second end of the base.
 7. The MEMS device of claim 1,wherein the base is a single unitary base.
 8. The MEMS device of claim1, wherein the plurality of mirrors are permanently attached to thebase.
 9. The MEMS device of claim 1, wherein the axis of rotation of thebase is aligned with a longitudinal axis of the base.
 10. A MEMS device,comprising: a single unitary base; and a plurality of mirror surfacespermanently placed on the single unitary base; the plurality of mirrorsurfaces being at respective angles relative to a reference surfacedefined by the single unitary base; wherein the respective angles of atleast some of the mirror surfaces are different from the respectiveangles of at least some others of the mirror surfaces; and therespective angles are permanently fixed relative to the referencesurface.
 11. The MEMS device of claim 10, wherein the reference surfaceis a flat bottom surface of the single unitary base.
 12. The MEMS deviceof claim 10, wherein at least two of the mirror surfaces are at a firstone of the respective angles relative to the reference surface.
 13. TheMEMS device of claim 10, wherein the mirror surfaces are arranged in aV-shaped pattern.
 14. The MEMS device of claim 13, wherein a pluralityof are nested together on the single unitary base.
 15. The MEMS deviceof claim 14, wherein at least a first one of the mirror surfaces is nearan apex of the corresponding V-shaped pattern; at least a second one ofthe mirror surfaces is near a lateral end of the corresponding V-shapedpattern; the first one of the mirror surfaces is at a first one of therespective angles; the second one of the mirror surfaces is at a secondone of the respective angles; and the first one of the respective anglesis steeper than the second one of the respective angles.
 16. The MEMSdevice of claim 10, wherein a first one of the V-shaped patterns is nearone edge of the single unitary base; a second one of the V-shapedpatterns is near an opposite edge of the single unitary base; and therespective angles of the mirror surfaces of the first one of theV-shaped patterns are greater than the respective angles of the mirrorsurfaces of the second one of the V-shaped patterns.
 17. The MEMS deviceof claim 16, wherein a third one of the V-shaped patterns is between thefirst one of the V-shaped patterns and the second one of the V-shapedpatterns; the respective angles of the mirror surfaces of the third oneof the V-shaped patterns are greater than the respective angles of themirror surfaces of the first one of the V-shaped patterns; and therespective angles of the mirror surfaces of the third one of theV-shaped patterns are less than the respective angles of the mirrorsurfaces of the second one of the V-shaped patterns.
 18. The MEMS deviceof claim 10, wherein the mirror surfaces are flat.
 19. The MEMS deviceof claim 10, wherein each of the mirror surfaces is rectangular and hasfour edges; two of the edges of each of the mirror surfaces are parallelwith two of the edges of others of the mirror surfaces; and the two ofthe edges of each mirror surface are at the respective angle of thecorresponding mirror surface.
 20. The MEMS device of claim 10, whereinthe mirror surfaces closer to one end of the single unitary base than anopposite end of the single unitary base are at lower respective anglesrelative to the reference surface than the mirror surfaces closer to theopposite end.
 21. The MEMS device of claim 20, wherein the respectiveangles progressively increase from the one end of the single unitarybase toward the opposite end of the single unitary base.